Magnetic field sensor based on topological insulator and insulating coupler materials

ABSTRACT

Embodiments are directed to a sensor having a first electrode, a second electrode and a detector region electrically coupled between the first electrode region and the second electrode region. The detector region includes a first layer having a topological insulator. The topological insulator includes a conducting path along a surface of the topological insulator, and the detector region further includes a second layer having a first insulating magnetic coupler, wherein a magnetic field applied to the detector region changes a resistance of the conducting path.

DOMESTIC PRIORITY

The application is a continuation of U.S. application Ser. No.15/609,647, filed May 31, 2017, which is a continuation of U.S.application Ser. No. 14/950,576, filed Nov. 24, 2015, now issued as U.S.Pat. No. 9,716,221, which is a continuation of U.S. application Ser. No.14/823,541, filed Aug. 11, 2015, now issued as U.S. Pat. No. 9,941,463,the contents of which are incorporated by reference herein in itsentirety.

BACKGROUND

The present disclosure relates generally to the field of semiconductormaterials and their fabrication. More specifically, the presentdisclosure relates to magnetic sensor semiconductor devices and methodsof operation and fabrication thereof that use as the detection mechanismthe response of a topological-insulator and an insulating coupler to amagnetic field having a particular magnitude and direction.

Magnetic sensors have a large range of potential applications,including, for example, biomedical detectors and non-volatile magneticmemory systems. Magnetic sensors operate based on an active sensingcomponent sensing the presence or absence of magnetic fields having aparticular magnitude and direction. The active sensing component sensesbased on quantum characteristics of the sensing component, such as theHall Effect, giant or tunnel magnetoresistance, or superconductingquantum interference. Such sensing components often require specialoperating environments, including, for example, low temperature or alarge bias. Additionally, magnetic sensors that utilize such sensingcomponents can require complex fabrication processes that limitscalability.

It has been proposed to use topological insulator material as the activesensing component of magnetic sensors. Topological insulator materials,such as mercury telluride (HgTe), bismuth selenide (Bi₂Se₃), or bismuthtelluride (Bi₂Te₃), exhibit quantum states of matter having timereversal symmetry, non-trivial topological order and a large band gapthat makes them suitable for room temperature applications. A materialthat exhibits topological insulator characteristics behaves as aninsulator in its interior but has conducting states at its surface,which means that electrons can only move along the surface of thematerial. More specifically, topological insulators possess aninsulating bulk/interior, wherein an energy gap separates the highestoccupied electronic valence energy band from the lowest empty conductionenergy band. Topological-insulators also exhibit gapless surface statesthat are due to a strong spin-orbit coupling of electrons. Time reversalsymmetry protects these conducting surface states from scattering byimpurities. In the presence of a sufficiently strong appliedperpendicular magnetic field, time-reversal symmetry is broken and anenergy gap emerges for these surface states, which results in a changein the resistance of the topological insulator material in response tothe magnetic field. Additionally, topological insulators demonstrate anon-saturating linear response to large magnetic fields due to weakanti-localization arising from strong spin-orbit coupling. Also, thetemperature range in which a topological insulator material caneffectively and reliably respond to an applied magnetic field can berelatively broad (i.e., ranging from absolute zero to 250 degreesCelsius).

Although topological insulators provide technical benefits when used asthe active sensing component of a magnetic sensor, there remain areassuch as sensitivity, overall performance and scalability in which theperformance of topological insulators in magnetic sensing applicationscan be improved. For example, the magnetic field that is required tobreak time reversal symmetry of a topological insulator material can berelatively large, typically in the range of approximately 20 Tesla.

SUMMARY

Embodiments are directed to a sensor having a first electrode, a secondelectrode and a detector region electrically coupled between the firstelectrode region and the second electrode region. The detector regionincludes a first layer having a topological insulator. The topologicalinsulator includes a conducing path along a surface of the topologicalinsulator, and the detector region further includes a second layerhaving a first insulating magnetic coupler, wherein a magnetic fieldapplied to the detector region changes a resistance of the conductingpath.

Embodiments are further directed to a method of forming a sensor. Themethod includes forming a first electrode, forming a second electrodeand forming a detector region. The method further includes electricallycoupling the detector region to the first electrode and the secondelectrode, and forming the detector region to include a first layercomprising a topological insulator. The topological insulator includes aconducing path along a surface of the topological insulator. The methodfurther includes forming the detector region to further include a secondlayer comprising a first insulating magnetic coupler, wherein a magneticfield applied to the detector region changes a resistance of theconducting path, and wherein the first insulating magnetic coupleramplifies the magnetic field applied to the detector region.

Additional features and advantages are realized through the techniquesdescribed herein. Other embodiments and aspects are described in detailherein. For a better understanding, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the present disclosure isparticularly pointed out and distinctly claimed in the claims at theconclusion of the specification. The foregoing and other features andadvantages are apparent from the following detailed description taken inconjunction with the accompanying drawings in which:

FIG. 1 depicts a three dimensional view of a semiconductor deviceaccording to one or more embodiments;

FIG. 2 depicts a three dimensional view of a semiconductor deviceaccording to one or more embodiments;

FIG. 3 depicts a three dimensional view of a semiconductor deviceaccording to one or more embodiments;

FIG. 4 depicts a three dimensional view of a semiconductor deviceaccording to one or more embodiments;

FIG. 5 depicts a three dimensional view of an array of semiconductordevices according to one or more embodiments;

FIG. 6 depicts a three dimensional view of an array of semiconductordevice according to one or more embodiments;

FIG. 7 depicts a cross sectional view of a semiconductor substrate afteran initial fabrication stage according to one or more embodiments;

FIG. 8 depicts a cross sectional view of an array of semiconductordevices after an intermediate fabrication stage according to one or moreembodiments;

FIG. 9 depicts a cross sectional view of an array of semiconductordevices after an intermediate fabrication stage according to one or moreembodiments;

FIG. 10 depicts a cross sectional view of an array of semiconductordevices after an intermediate fabrication stage according to one or moreembodiments;

FIG. 11 depicts a cross sectional view of an array of semiconductordevices after an intermediate fabrication stage according to one or moreembodiments;

FIG. 12 depicts a cross sectional view of an array of semiconductordevices according to one or more embodiments; and

FIG. 13 depicts a flow diagram illustrating a methodology according toone or more embodiments.

In the accompanying figures and following detailed description of thedisclosed embodiments, the various elements illustrated in the figuresare provided with three or four digit reference numbers. The leftmostdigit(s) of each reference number corresponds to the figure in which itselement is first illustrated.

DETAILED DESCRIPTION

Various embodiments of the present disclosure will now be described withreference to the related drawings. Alternate embodiments may be devisedwithout departing from the scope of this disclosure. It is noted thatvarious connections are set forth between elements in the followingdescription and in the drawings. These connections, unless specifiedotherwise, may be direct or indirect, and the present disclosure is notintended to be limiting in this respect. Accordingly, a coupling ofentities may refer to either a direct or an indirect connection.

Similarly, although the operations of methodologies disclosed herein areillustrated in a particular order, it will be understood by persons ofordinary skill in the relevant art that the order of the illustratedoperations may be changed without departing from the teachings of thepresent disclosure. In addition, it will be understood by persons ofordinary skill in the relevant art that one or more of the illustratedoperations may be omitted, and/or operations not shown (e.g., routineintermediary operations) may be incorporated, without departing from theteachings of the present disclosure.

For the sake of brevity, conventional techniques related tosemiconductor device fabrication may not be described in detail herein.Moreover, the various tasks and process steps described herein may beincorporated into a more comprehensive procedure or process havingadditional steps or functionality not described in detail herein. Inparticular, various steps in the manufacture of semiconductor baseddevices are well known and so, in the interest of brevity, manyconventional steps may only be mentioned briefly herein or may beomitted entirely without providing the well-known process details.

As previously noted herein, magnetic sensors have a large range ofpotential applications, including, for example, biomedical detectors andnon-volatile magnetic memory systems. Magnetic sensors operate based onan active sensing component sensing the presence or absence of magneticfields having a particular magnitude and direction. The active sensingcomponent may be based on quantum characteristics of the sensingcomponent, such as the Hall Effect, giant or tunnel magnetoresistance,or superconducting quantum interference. Such sensing components oftenrequire special operating environments, including, for example, lowtemperature or a large bias. Additionally, magnetic sensors that utilizethese sensing components can require complex fabrication processes thatlimit scalability.

It is known to use a topological insulator as the active sensingcomponent of a magnetic sensor. A topological insulator is a materialwith non-trivial topological order that behaves as an insulator in itsinterior. However, the surface of a topological insulator containsconducting states, which means that electrons can only move along thesurface of the material. Although ordinary band insulators can alsosupport conductive surface states, the surface states of topologicalinsulators are unique because they are symmetry protected by particlenumber conservation and time reversal symmetry. More specifically, inthe bulk/interior of a non-interacting topological insulator, theelectronic band structure resembles an ordinary band insulator (i.e.,the Fermi level falls between the conduction and valence bands).However, on the surface of a topological insulator there are specialstates that fall within the bulk energy gap and allow surface metallicconduction. Carriers in these surface states have their spin locked at aright-angle to their momentum, which is known generally as spin-momentumlocking. At a given energy the only other available electronic stateshave different spin, which suppresses scattering and causes conductionon the surface of the material to be highly metallic. The surfaceconduction states are required by time-reversal symmetry and the bandstructure of the material. These surface conducting states can beremoved by breaking the topological insulator's time-reversal symmetry,which does not happen with potential and/or spin-orbit scattering, butinstead happens in the presence of a sufficiently strong (e.g.,approximately 20 Tesla) magnetic field.

An exemplary two terminal magnetic sensor device that incorporates athin-film topological insulator as the active sensing element isdescribed in a co-pending, commonly assigned U.S. patent application,titled “Thin Film Device With Protective Layer,” having application Ser.No. 14/571,771, filed on Dec. 16, 2014, the entire disclosure of whichis incorporated by reference herein.

Turning now to a more general overview of the present disclosure, one ormore disclosed embodiments provide magnetic sensor semiconductor devicesand methods of operation and fabrication thereof that use as thedetection mechanism the response of a topological-insulator having aninsulating coupler to a magnetic field having a particular magnitude anddirection. In one or more embodiments, the sensor includes a thin-filmtopological insulator grown using a technique such as molecular beamepitaxy. The topological insulator is contacted on both ends by metalelectrodes to form a two-terminal electrical device. The thin-filmtopological insulator may include a large surface-to-volume ratio, andmay also include magnetic doping. The insulating magnetic coupler isprovided above, below or around (i.e., both above and below) thethin-film topological insulator.

When a bias voltage is applied between the electrodes, and when nomagnetic field is applied, a current flows through the topologicalinsulator surface states between the electrodes. When a magnetic fieldis introduced, for example, a magnetic field exceeding a certainmagnitude and pointed perpendicular to the topological insulatorsurface, the topological insulator surface states develop an energy gapand are no longer conducting, which reduces the current flow, increasesresistance and produces a measurable change. This measureable change inthe magnetic sensing component (i.e., topological insulator) can be usedin a variety of sensing and/or switching applications such as biomedicaldetectors and non-volatile magnetic memory systems.

The magnitude of the magnetic field that is required to break timereversal symmetry of known thin-film topological insulator materialsmust be relatively large, typically in the range of approximately 20Tesla. According to one or more embodiments, the insulating magneticcoupler is sufficiently close to the thin-film topological insulator toamplify the applied magnetic field based at least in part on a magneticexchange effect between the insulating magnetic coupler and thethin-film topological insulator. Accordingly, a magnetic sensoraccording to the present disclosure can respond to relatively smallapplied perpendicular magnetic field magnitudes (e.g., 0.10 Tesla)because the insulating magnetic coupler amplifies the appliedperpendicular magnetic field magnitude to a level that is sufficient tobreak time reversal symmetry of the thin film topological insulatorsensing mechanism, thereby causing a measureable change in the thin filmtopological insulator's conductance/resistance. The insulating magneticcoupler may contact the thin film topological insulator, or it may bepositioned sufficiently close to the thin film topological insulator toeffect a magnetic exchange between the insulating magnetic coupler andthe thin film topological insulator. As noted above, the insulatingmagnetic coupler may be above, below or both above and below thethin-film topological insulator.

Materials that can serve as the insulating magnetic coupler include, forexample, europium sulfide, europium oxide, hollandite chromium oxide(low-temperature operations), yttrium iron garnet, or acobalt-iron-aluminum-oxide multilayer (for room-temperature and aboveoperation). For the cobalt-iron-aluminum-oxide multilayerimplementation, the crystal structure templating, oxidationmethod/duration, and annealing conditions determine its magneticproperties. The insulating properties generally come from the oxygenpresent in the structure. These materials can also be doped with otherelements (such as lanthanum, neodymium, cadmium, or vanadium) to enhancetheir magnetic properties and they can generally be synthesized usingseveral techniques, including sputtering, molecular beam epitaxy, andpulsed laser deposition.

As described above, in one or more embodiments, the topologicalinsulator may be doped/implanted with magnetic atoms/particles. In suchembodiments, in addition to the amplification provided by the insulatingmagnetic coupler, the applied perpendicular magnetic field magnitude iseven further amplified by the magnetic particles. The implanted magneticparticles may be applied to the bulk/interior, the surface state or boththe bulk and the surface state areas of the thin-film topologicalinsulator. The implanted magnetic particles further enhance the couplingof an applied magnetic field to the thin-film topological insulatorsurface. The magnetic particles can have randomly oriented individualmagnetic moments, but when in the presence of an outside magnetic field,the magnetic moments of these particles can align with a sizablemagnetic moment and induce a much stronger magnetic coupling to thethin-film topological insulator.

In one or more embodiments, an array of the disclosed magnetic sensorsemiconductor devices may be formed at a nanoscale level on a substrateand ribbed metallic electrode structures and capped with anotherinsulating magnetic coupler layer or a conformal cap (e.g.,silicon-nitride) to vacuum protect the magnetic sensor surfaces in amanner that is compatible with standard CMOS integration. Each magneticsensor (i.e., pixel) of the array can be individually addressed fordetection readout. Additionally, conformal growth of topologicalinsulator materials on both the ribbed metal structure and the substratecan provide an extra vertical topological insulator section of thedevice, which may be utilized to detect magnetic fields in additionaldimensions. For example, such a magnetic sensor configuration cansimultaneously detect fields pointing out-of-plane (i.e., perpendicularto the substrate) and in-plane (i.e., parallel to the substrate, orperpendicular to the ribbed side of the substrate).

Accordingly, a magnetic sensor according to the present disclosureoperates with increased sensitivity over a broader range of appliedmagnetic field strengths (e.g., from about 0.10 Tesla to about 20Tesla), which also allows for operation over a broader range oftemperatures (e.g., from absolute zero to 250 degrees Celsius). Thereare no intrinsic size requirements for the disclosed magnetic sensor.The disclosed magnetic sensor is intrinsically scalable because itbecomes more sensitive as it becomes smaller, and because it does nothave a net magnetic moment and therefore there are no offset fields tocancel. The disclosed magnetic sensor device possesses low-powerrequirements because only a small bias current is needed to readout thedevice.

Turning now to a more detailed description of the present disclosure,FIGS. 1-4 depict three dimensional views of a magnetic sensorsemiconductor device 100 according to one or more embodiments. Magneticsensor 100 includes a substrate 102, a thin-film topological insulatorlayer 104, a first insulating magnetic coupler layer 106, a firstelectrode 108 and a second electrode 110, configured and arranged asshown. FIG. 1 depicts magnetic sensor 100 in its steady state, wherein abias voltage is present across first and second electrodes 108, 110, nomagnetic field is present and a current 112 (shown in FIG. 2) flowsalong a surface of thin-film topological insulator 104 from firstelectrode 108 to second electrode 110. FIG. 2 depicts the steady stateof magnetic sensor 100 shown in FIG. 1, wherein first insulatingmagnetic coupler layer 106 is shown, for illustration purposes,separated away from topological insulator layer 104 in order toillustrate current 112 flowing along a surface of topological insulatorlayer 104.

FIGS. 3 and 4 depict magnetic sensor 100 when an out-of-plane magneticfield 114 of sufficient magnitude (e.g., greater than about 0.10 Tesla)is present. Similar to FIGS. 1 and 2, FIG. 3 depicts thin-filmtopological insulator layer 104 adjacent first insulating magneticcoupler layer 106, and FIG. 4 depicts first insulating magnetic couplerlayer 106, for illustration purposes, separated away from topologicalinsulator layer 104 in order to illustrate that current has beensignificantly reduced or is no longer flowing along a surface oftopological insulator layer 104. As shown in FIGS. 3 and 4, in thepresence of magnetic field 114, the surface states of thin-filmtopological insulator layer 104 develop an energy gap, which ceases orsubstantially reduces current flow (112 shown in FIG. 2), increasesresistance and produces a measurable change. The measureable change inthe resistance of the surface states of thin-film topological insulatorlayer 104 allows magnetic sensor 100 to be used in a variety of sensingand/or switching applications such as biomedical detectors and innon-volatile magnetic memory systems.

First insulating magnetic coupler layer 106 is sufficiently close tothin-film topological insulator layer 104 to amplify applied magneticfield 114 based at least in part on a magnetic exchange effect betweenfirst insulating magnetic coupler layer 106 and thin-film topologicalinsulator layer 106. Accordingly, magnetic sensor 100 according to thepresent disclosure can respond to an applied magnetic field (e.g.,magnetic field 114) having a relatively small magnitude (e.g., about0.10 Tesla) because first insulating magnetic coupler layer 106amplifies the magnitude of applied perpendicular magnetic field 114 to alevel that is sufficient to break time reversal symmetry of thin-filmtopological insulator layer 104, thereby causing a measureable change ina conductance/resistance of thin-film topological insulator layer 104.

First insulating magnetic coupler layer 106 is shown in FIG. 1 incontact with thin-film topological insulator layer 106. Alternatively,thin-film topological insulator layer 106 may be positioned sufficientlyclose to thin-film topological insulator layer 104 to effect a magneticexchange between first insulating magnetic coupler layer 106 andthin-film topological insulator layer 104. Additionally, firstinsulating magnetic coupler layer 106 is shown above thin-filmtopological insulator layer 104. Alternatively, insulating magneticcoupler layer 106 may be positioned above, below or both above and belowthin-film topological insulator layer 104.

In one or more embodiments, in addition to the amplification provided byfirst insulating magnetic coupler layer 106, the magnitude of appliedperpendicular magnetic field 114 may be even further amplified bydoping/implanting thin film topological insulator layer 104 withmagnetic atoms/particles (not shown). The implanted magnetic particlesmay be applied to the interior area, the surface state area or both theinterior and the surface state areas of thin-film topological insulatorlayer 104. As previously described herein, the implanted magneticparticles further enhance the coupling of applied magnetic field 114 tothin-film topological insulator layer 104 because the implanted magneticparticles can have randomly oriented individual magnetic moments, butwhen in the presence of an outside magnetic field (e.g., magnetic field114), the magnetic moments of these particles can align with a sizablemagnetic moment and induce a much stronger magnetic coupling tothin-film topological insulator layer 104.

FIG. 5 depicts a three-dimensional view of magnetic sensor semiconductordevices configured as an array 500 according to one or more embodiments.The structure and operation of the magnetic sensor devices shown in FIG.5 substantially correspond to the structure and operation of magneticsensor 100 shown in FIGS. 1-4 with the addition of a second insulatingmagnetic coupler layer 502 located below thin-film topological insulatorlayer 104. Additionally, first and second electrodes 108, 110 areimplemented as ribbed metallic structures. Second insulating magneticcoupler layer 502 provides magnetic field amplification in addition to,and in a manner substantially the same as, the magnetic fieldamplification provided by first insulating magnetic coupler layer 106.For ease of illustration, only one of the three magnetic sensor devicesshown in FIG. 5 is provided with reference numbers. Additionally,although an insulating magnetic coupler layer (106, 502) is shown aboveand below topological insulator layer 104, an insulating magneticcoupler layer may also be provided only above or only below topologicalinsulator layer 104 of the magnetic sensor shown in FIG. 5. Eachmagnetic sensor of array 500 can be individually addressed for detectionreadout.

In one or more embodiments, in addition to the amplification provided byfirst insulating magnetic coupler layer 106 and second insulatingmagnetic coupler layer 502, the magnitude of applied perpendicularmagnetic field 114 (shown in FIGS. 2 and 4) may be even furtheramplified by doping/implanting thin film topological insulator layer 104with magnetic atoms/particles (not shown). The implanted magneticparticles may be applied to the interior area, the surface state area orboth the interior and the surface state areas of thin-film topologicalinsulator layer 104. As previously described herein, the implantedmagnetic particles further enhance the coupling of applied magneticfield 114 to thin-film topological insulator layer 104 because theimplanted magnetic particles can have randomly oriented individualmagnetic moments, but when in the presence of an outside magnetic field(e.g., magnetic field 114), the magnetic moments of these particles canalign with a sizable magnetic moment and induce a much stronger magneticcoupling to thin-film topological insulator layer 104.

FIG. 6 depicts a three-dimensional view of magnetic sensor semiconductordevices configured as an array 600 according to one or more embodiments.The structure and operation of the magnetic sensor devices shown in FIG.6 substantially correspond to the structure and operation of themagnetic sensors shown in FIG. 5 with the addition of a third insulatingmagnetic coupler layer 602 or a conformal cap (e.g., silicon-nitride) toform vacuum areas 604 that protect the surfaces of the magnetic sensorsin a manner that is compatible with standard CMOS integration. For easeof illustration, only one of the three magnetic sensor devices of array600 is provided with reference numbers. Additionally, although aninsulating magnetic coupler layer (106, 502) is shown above and belowtopological insulator layer 104, an insulating magnetic coupler layermay also be provided only above or only below topological insulatorlayer 104 of the magnetic sensor shown in FIG. 6. Each magnetic sensorof array 600 can be individually addressed for detection readout.

Similar to array 500, for the magnetic sensors of array 600, in additionto the amplification provided by first insulating magnetic coupler layer106 and second insulating magnetic coupler layer 502, the magnitude ofapplied perpendicular magnetic field 114 (shown in FIGS. 2 and 4) may beeven further amplified by doping/implanting thin film topologicalinsulator layer 104 with magnetic atoms/particles (not shown). Theimplanted magnetic particles may be applied to the interior area, thesurface state area or both the interior and the surface state areas ofthin-film topological insulator layer 104. As previously describedherein, the implanted magnetic particles further enhance the coupling ofapplied magnetic field 114 to thin-film topological insulator layer 104because the implanted magnetic particles can have randomly orientedindividual magnetic moments, but when in the presence of an outsidemagnetic field (e.g., magnetic field 114), the magnetic moments of theseparticles can align with a sizable magnetic moment and induce a muchstronger magnetic coupling to thin-film topological insulator layer 104.

FIG. 12 depicts a two-dimensional view of magnetic sensor semiconductordevices configured as an array 1200 according to one or moreembodiments. The structure and operation of the magnetic sensor devicesshown in FIG. 12 substantially correspond to the structure and operationof the magnetic sensors shown in FIGS. 5 and 6 with the addition ofthin-film topological insulator layer 104 and first and secondinsulating magnetic coupler layers 106, 502 grown conformally overribbed metallic electrodes 108, 110 and substrate 102. Conformal growthof topological insulator layer 104 over both ribbed metallic electrodestructures 108, 110 and substrate 102 can provide an extra verticaltopological insulator section of the magnetic sensor device, which maybe utilized to detect magnetic fields in additional dimensions. Forexample, such a magnetic sensor configuration can simultaneouslydetecting fields pointing out-of-plane (i.e., perpendicular to thesubstrate) (e.g., magnetic field 114) and in-plane (i.e., parallel tothe substrate, or perpendicular to the ribbed side of the substrate)(e.g., magnetic field 1202). For ease of illustration, only one of thethree magnetic sensor devices of array 1200 is provided with referencenumbers. Additionally, although an insulating magnetic coupler layer(106, 502) is shown above and below topological insulator layer 104, aninsulating magnetic coupler layer may also be provided only above oronly below topological insulator layer 104 of the magnetic sensor shownin FIG. 12. Each magnetic sensor of array 1200 can be individuallyaddressed for detection readout.

Similar to arrays 500, 600, for the magnetic sensors of array 1200, inaddition to the amplification provided by first insulating magneticcoupler layer 106 and second insulating magnetic coupler layer 502, themagnitudes of applied perpendicular magnetic field 114 (shown in FIGS. 2and 4) and applied parallel magnetic field 1202 may be even furtheramplified by doping/implanting thin film topological insulator layer 104with magnetic atoms/particles (not shown). The implanted magneticparticles may be applied to the interior area, the surface state area orboth the interior and the surface state areas of thin-film topologicalinsulator layer 104. As previously described herein, the implantedmagnetic particles further enhance the coupling of applied magneticfield 114 and applied magnetic field 1202 to thin-film topologicalinsulator layer 104 because the implanted magnetic particles can haverandomly oriented individual magnetic moments, but when in the presenceof an outside magnetic field (e.g., magnetic field 114 and/or magneticfield 1202), the magnetic moments of these particles can align with asizable magnetic moment and induce a much stronger magnetic coupling tothin-film topological insulator layer 104.

FIGS. 7-12 depict various fabrication stages in forming array 1200 shownin FIG. 12. FIG. 7 depicts semiconductor substrate 102 upon whichembodiments of the present disclosure can be fabricated. Semiconductorsubstrate 102 is preferably composed of a silicon (Si) containingmaterial. Silicon containing materials include, but are not limited to,Si, single crystal Si, polycrystalline Si, silicon-germanium (SiGe),single crystal SiGe, polycrystalline SiGe, or Si doped with carbon (C),amorphous Si and combinations and multi-layers thereof. Semiconductorsubstrate 102 can also be composed of other semiconductor materials,such as Ge, and compound semiconductor substrates such as type III/Vsemiconductor substrates, e.g., gallium arsenide (GaAs) or indiumphosphide (InP). In general, semiconductor substrate 102 is a smoothsurface substrate. In some embodiments (not shown), semiconductorsubstrate 102 can be a partially processed complementarymetal-oxide-semiconductor (CMOS) integrated wafer with transistors andwiring levels or gate electrodes embedded beneath the surface.

In FIG. 8, ribbed metal electrodes (e.g., 108, 110) are formed on top ofsemiconductor substrate 102 using techniques known in the art. In oneembodiment, ribbed metal electrodes are formed using a photolithographicand subtractive etching process to define the structure of the ribbedmetal. Photolithography is a process to pattern parts of a thin film orthe bulk of a substrate. For example, a metal layer can be initiallyformed on top of semiconductor substrate 102, and ribbed metalelectrodes (e.g., 108, 110) may be formed by selective etching of themetal layer. The ribbed metal electrodes can be composed of differenttypes of metal, such as, but not limited to, copper, aluminum, gold,palladium or any other conductive material. In some embodiments, theribbed metal electrodes have a nonmetallic, and/or nonconductive toplayer (not shown). In general, individual ribs (not shown) of the ribbedmetal electrodes act as terminals for the resulting magnetic sensordevices of array 1200. In some embodiments, individual ribs of theribbed metal electrodes act as a shunt between sections of the resultingmagnetic sensor devices of array 1200 that are in contact withsemiconductor substrate 102.

In some embodiments, each rib of the ribbed metal electrodes is of thesame type of metal. In other embodiments, individual portions of theribbed metal electrodes can be different types of metal. In someembodiments, individual portions of the ribbed metal electrodes aredisposed on top of semiconductor substrate 102 in a periodic order. Inother embodiments, individual portions of the ribbed metal electrodesare disposed on top of semiconductor substrate 102 in an aperiodicorder.

In some embodiments, individual portions of the ribbed metal electrodesmake electrical contact with a circuit, such as a readout circuit,located at the end of or beneath respective ribs. For example, eachportion of the ribbed metal electrodes can be an elongated, rod-likemember or structure that extends to, or near, the edge of semiconductorsubstrate 102 and can make electrical contact with a circuit located atthe described location. In other embodiments, individual portions of theribbed metal electrodes form islands on top of semiconductor substrate102. In such an embodiment, individual portions of the ribbed metalelectrodes can be connected to transistors through semiconductorsubstrate 102, such as, for example, when semiconductor substrate 102 isa partially processed CMOS-integrated wafer with transistors and wiringlevels or gate electrode (not shown) beneath the surface ofsemiconductor substrate 102.

In FIG. 9, second insulating magnetic coupler layer 502 is formed on topof ribbed metal electrodes (e.g., 108, 110) and substrate 102 in aconformal fashion. Second insulating magnetic coupler layer 502 may beany material or combination of materials that exhibit both insulatingproperties and magnetic coupling properties. Second insulating magneticcoupler layer 502 may be formed using deposition methods known in theart. The specific type of deposition method used to deposit secondmagnetic coupler layer 502 can vary based upon the specific material(s)that comprise second insulating magnetic coupler layer 502. For example,second insulating magnetic coupler layer 502 can be deposited via directtransfer, spin coating, evaporation, sputtering, or other techniquesknown in the art, in accordance with the selected material of secondinsulating magnetic coupler layer 502, in accordance with the embodimentof the present disclosure. Second insulating magnetic coupler layer 502may be implemented as a multi-layer element, as desired for particularapplications.

In FIG. 10, thin-film topological insulator layer 104 is formed on topof second insulating magnetic coupling layer 502 in a conformal fashion.Thin-film topological insulator layer 104 can be, for example, atopological insulator, graphene, carbon nanotubes, transition metaldichalcogenide monolayers, hexagonal boron nitride, or boron nanotubes.Similar to second insulating magnetic coupler layer 502, thin-filmtopological insulator layer 104 may be formed using deposition methodsknown in the art. The specific type of deposition method used to depositthin-film topological insulator layer 104 can vary based upon thespecific material(s) that comprise thin-film topological insulator layer104. For example, thin-film topological insulator layer 104 can bedeposited via direct transfer, spin coating, evaporation, sputtering, orother techniques known in the art, in accordance with the selectedmaterial of thin-film topological insulator layer 104, in accordancewith the embodiment of the present disclosure. Thin-film topologicalinsulator layer 104 may be implemented as a multi-layer element, asdesired for particular applications. In some embodiments, a chemical orother type of surface preparation is used on thin-film topologicalinsulator layer 104, or a seed layer is deposited. Such preparation canfacilitate increased ohmic electrical contact between thin filmtopological insulator 104 and the ribbed metal electrodes (e.g., 108,110).

In FIG. 11, first insulating magnetic coupler layer 502 is formed on topof thin-film topological insulator layer 104 in a conformal fashion.First insulating magnetic coupler layer 104 may be any material orcombination of materials that exhibit both insulating properties andmagnetic coupling properties. First insulating magnetic coupler layer104 may be formed using deposition methods known in the art. Thespecific type of deposition method used to deposit first magneticcoupler layer 104 can vary based upon the specific material(s) thatcomprise first insulating magnetic coupler layer 104. For example, firstinsulating magnetic coupler layer 104 can be deposited via directtransfer, spin coating, evaporation, sputtering, or other techniquesknown in the art, in accordance with the selected material of firstinsulating magnetic coupler layer 104, in accordance with the embodimentof the present disclosure. First insulating magnetic coupler layer 104may be implemented as a multi-layer element, as desired for particularapplications.

Materials that can serve as first or second insulating magnetic couplerlayers 106, 502 include, for example, europium sulfide, europium oxide,hollandite chromium oxide (low-temperature operations), yttrium irongarnet, or a cobalt-iron-aluminum-oxide multilayer (for room-temperatureand above operation). For the cobalt-iron-aluminum-oxide multilayerimplementation, the crystal structure templating, oxidationmethod/duration, and annealing conditions determine its magneticproperties. The insulating properties generally come from the oxygenpresent in the structure. These materials can also be doped with otherelements (such as lanthanum, neodymium, cadmium, or vanadium) to enhancetheir magnetic properties and they can generally be synthesized usingseveral techniques, including sputtering, molecular beam epitaxy, andpulsed laser deposition.

In FIG. 12, a third insulating magnetic coupler layer 602 or a conformalcap (e.g., silicon-nitride) is formed over the ribbed metallicelectrodes (e.g., 108, 110) to form vacuum areas 604 that protect thesurfaces of the magnetic sensors in a manner that is compatible withstandard CMOS integration. Capping layer 602 can be a dielectricmaterial. For example, capping layer 602 can be oxide, nitride, siliconnitride, or any other dielectric material. In general, capping layer 602is deposited such that at least one enclosed space, such as enclosedspace 604, is created. In some embodiments, capping layer 602 isdeposited in a non-conformal manner. In other embodiments, capping layer602 is deposited in a semi-conformal manner. In some embodiments,capping layer 602 is deposited such that capping layer 602 contacts thetop surface of portions of the ribbed metal electrodes (e.g., 108, 110).In general, capping layer 602 is deposited such that capping layer 602does not contact one or more portions of first and second insulatingmagnetic coupler layers 106, 502 and thin film topological insulatorlayer 104 that are in contact with semiconductor substrate 102 and arebetween two portions of the ribbed metal electrodes.

In some embodiments, capping layer 602 is deposited while the device isin a vacuum, or substantial vacuum. For example, capping layer 602 canbe deposited while the device is in a vacuum chamber. In otherembodiments, capping layer 602 is deposited while the device is exposedto an inert gas.

In some embodiments, enclosed spaces, such as enclosed space 604, arevacuum pockets. Vacuum pockets that exist as enclosed spaces, such asenclosed space 604, act to protect the surface of portions of firstand/or second insulating magnetic coupler layers 106, 502 and/orthin-film topological insulator layer 104 within the enclosed spaces(e.g., within enclosed space 604). In general, the vacuum pockets aresubstantially free of gases or other materials. Ideally, a vacuum pocketwill be an enclosed space, such as enclosed space 604, which exists in avacuum. In other embodiments, enclosed spaces, such as enclosed space604, are filled with an inert gas, such as a noble gas (e.g., helium,neon, argon, krypton, xenon, or radon), or a compound gas, such as acompound gas containing argon. An inert gas can provide structuraland/or chemical stability to the portions of thin-film topologicalinsulator layer 104 within the enclosed spaces (e.g., within enclosedspace 604). In general, enclosed spaces, such as enclosed space 604protect the active material (e.g., layers 502, 104, 106) of the magneticsensing devices of array 1200 from external environmental impurities andeffects.

FIG. 13 depicts a flow diagram illustrating a methodology 1300 forforming a magnetic sensor according to one or more embodiments of thepresent disclosure. Methodology 1300 begins a block 1302 by forming asubstrate. Block 1304 forms at least two metal electrodes, and block1306 forms a topological insulator. Block 1308 forms at least oneinsulating magnetic coupler layer. In accordance with one or moreembodiments, the insulating magnetic coupler is sufficiently close tothe topological insulator to amplify an applied magnetic field based atleast in part on a magnetic exchange effect between the insulatingmagnetic coupler and the topological insulator. Accordingly, a magneticsensor according to methodology 1300 can respond to relatively smallapplied magnetic field magnitudes (e.g., 0.10 Tesla) because theinsulating magnetic coupler amplifies the applied magnetic fieldmagnitude to a level that is sufficient to break time reversal symmetryof the topological insulator sensing mechanism, thereby causing ameasureable change in the thin film topological insulator'sconductance/resistance. The insulating magnetic coupler may contact thetopological insulator, or it may be positioned sufficiently close to thetopological insulator to effect a magnetic exchange between theinsulating magnetic coupler and the topological insulator. Theinsulating magnetic coupler may be above, below or both above and belowthe topological insulator.

Methodology 1300 may optionally include doping the topological insulatorwith doped/implanted magnetic atoms/particles. In addition to theamplification provided by the insulating magnetic coupler, the appliedmagnetic field magnitude is even further amplified by the magneticparticles. The implanted magnetic particles may be applied to thebulk/interior, the surface state or both the bulk and the surface stateareas of the topological insulator.

Methodology 1300 may be repeated to form an array of the disclosedmagnetic sensor semiconductor devices at a nanoscale level on thesubstrate and on ribbed metallic electrode structures and capped withanother insulating magnetic coupler layer or a conformal cap (e.g.,silicon-nitride) to vacuum protect the magnetic sensor surfaces in amanner that is compatible with standard CMOS integration. Each magneticsensor (i.e., pixel) of the array can be individually addressed fordetection readout. Additionally, conformal growth of topologicalinsulator materials on both the ribbed metal structure and the substratecan provide an extra vertical topological insulator section of thedevice, which may be utilized to detect magnetic fields in additionaldimensions. For example, such a magnetic sensor configuration cansimultaneously detecting fields pointing out-of-plane (i.e.,perpendicular to the substrate) and in-plane (i.e., parallel to thesubstrate, or perpendicular to the ribbed side of the substrate).

Thus it can be seen from the foregoing detailed description that thepresent disclosure provides a number of technical benefits. A magneticsensor according to the present disclosure operates with increasedsensitivity over a broader range of applied magnetic field strengths(e.g., from about 0.10 Tesla to about 20 Tesla), which also allows foroperation over a broader range of temperatures (e.g., from absolute zeroto 250 degrees Celsius). There are no intrinsic size requirements forthe disclosed magnetic sensor. The disclosed magnetic sensor isintrinsically scalable because it becomes more sensitive as it becomessmaller, and because it does not have a net magnetic moment andtherefore there are no offset fields to cancel. The disclosed magneticsensor device possesses low-power requirements because only a small biascurrent is needed to readout the device.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprises” and/or “comprising,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, element components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thepresent disclosure has been presented for purposes of illustration anddescription, but is not intended to be exhaustive or limited to the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art without departing from the scope and spiritof the disclosure. The embodiments were chosen and described in order tobest explain the principles of the disclosure and the practicalapplication, and to enable others of ordinary skill in the art tounderstand the disclosure for various embodiments with variousmodifications as are suited to the particular use contemplated.

The diagrams depicted herein are illustrative. There may be manyvariations to the diagram or the steps (or operations) described thereinwithout departing from the spirit of the disclosure. For instance, theactions may be performed in a differing order or actions may be added,deleted or modified. Also, the term “coupled” describes having a signalpath between two elements and does not imply a direct connection betweenthe elements with no intervening elements/connections therebetween. Allof these variations are considered a part of the disclosure.

It will be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow.

What is claimed is:
 1. A method of forming a sensor, the methodcomprising: forming a first electrode region; forming a second electroderegion; forming a detector region; electrically coupling the detectorregion to the first electrode and the second electrode; forming thedetector region to include a first layer comprising a topologicalinsulator; the topological insulator having an insulating region in abody of the topological insulator; the topological insulator furtherhaving a conducing path along a surface of the topological insulator,wherein a steady state condition of the topological insulator comprisesthe insulation region acting as an insulator and the conducting pathalong the surface of the topological insulator acting as a currentconductor; and forming the detector region to further include a secondlayer comprising a first insulating magnetic coupler; wherein a magneticfield applied to the detector region is sufficient to change the steadystate condition of the topological insulator by developing energy gapsin the conducting path along the surface of the topological insulatorthat are sufficient to change a resistance of the conducting path. 2.The method of claim 1, wherein the first insulating magnetic coupleramplifies the magnetic field applied to the detector region.
 3. Themethod of claim 2, wherein: the topological insulator comprisesimplanted magnetic particles; and the implanted magnetic particlesamplify the magnetic field applied to the detector region.
 4. The methodof claim 2 further comprising: forming the detector region to furthercomprise a third layer comprising a second insulating magnetic coupler;wherein the second insulating magnetic coupler amplifies the magneticfield applied to the detector region.
 5. The method of claim 1 furthercomprising forming a vacuum enclosure over at least a surface of thedetector region.
 6. The method of claim 1 further comprising: forming asubstrate; wherein the surface of the topological insulator is formedby: forming a horizontal region that is substantially parallel to asurface of the substrate; and forming a vertical region that issubstantially perpendicular to the surface of the substrate: wherein themagnetic field applied to the detector region comprises a magnetic fieldperpendicular the horizontal region or a magnetic field perpendicularthe vertical region.
 7. The method of claim 1, wherein the detectorregion comprises a third layer comprising a second insulating magneticcoupler.
 8. The method of claim 7, wherein the second insulatingmagnetic coupler amplifies the magnetic field applied to the detectorregion.
 9. The method of claim 8, wherein the second insulating coupleramplifies the magnetic field based at least in part on a magneticexchange effect between the first layer and the third layer.
 10. Amethod of forming a sensor, the method comprising: forming a firstelectrode region; forming a second electrode region; forming a detectorregion; and electrically coupling the detector region to the firstelectrode region and the second electrode region; the detector regioncomprising a first layer comprising a topological insulator; thetopological insulator having an insulating region in a body of thetopological insulator; the topological insulator further having aconducing path along a surface of the topological insulator, wherein asteady state condition of the topological insulator comprises theinsulation region acting as an insulator and the conducting path alongthe surface of the topological insulator acting as a current conductor;the detector region further comprising a second layer comprising a firstinsulating magnetic coupler; wherein a magnetic field applied to thedetector region is sufficient to change a resistance of the conductingpath by: developing energy gaps in the conducting path along the surfaceof the topological insulator that are sufficient to change a resistanceof the conducting path along the surface of the topological insulator;and breaking a time-reversal symmetry characteristic of the topologicalinsulator.
 11. The method of claim 10, wherein the first insulatingmagnetic coupler amplifies the magnetic field applied to the detectorregion based at least in part on a magnetic exchange effect between thefirst layer and the second layer.
 12. The method of claim 10, wherein:the detector region comprises a third layer comprising a secondinsulating magnetic coupler.
 13. The method of claim 10, wherein thesecond insulating magnetic coupler amplifies the magnetic field appliedto the detector region.
 14. The method of claim 13, wherein the secondinsulating coupler amplifies the magnetic field based at least in parton a magnetic exchange effect between the first layer and the thirdlayer.